This invention relates to roofing flashing and more particularly to a unique roof drain flashing material.
Conventionally, roof drain flashing materials have for decades been primarily composed of roofing felts hot mopped into the drain body on low cost installations, or of metal such as copper or preferably lead on more costly installations. As is well known, the mopped roofing paper type flashing does not effectively accommodate thermal expansion and contraction for the life of the roof in the critical areas around projections such as drain stacks, where most leakage begins. Metal materials, though heavy and expensive, have thermal accommodation but require periodic remopping of tar over the peripheral portions for resealing because of the lack of a bond of the metal to the adjacent roof membrane material. Periodic remopping necessarily results in a build-up of tar that forms a dam which prevents complete drainage of surrounding roof water. The retained roof water is subject to freezing and the like to create other problems.
In recent years, efforts have been made to develop flashing materials that would not be as expensive as metal and would be superior to impregnated paper. In U.S. Pat. No. 3,641,216 is taught a polymeric material that has flexibility without the necessity of plasticizers so as to not become inflexible like vinyl materials which contain plasticizers and have a high percent of liquids in the compound. This patented material, produced by The Dow Chemical Company, contains no plasticizers, and therefore no nutrient to support growth of fungus, algae or other micro-organisms which would biodegrade the sheet.
CPE sheet has very low temperature flexibility, ability to conform to irregular surfaces, high tensile strength, high elongation, and capacity for solvent welding. If the CPE sheet is simply mopped in unprotected, telegraphic cracks will occur when the asphalt cracks because hot asphalt bonds very well to CPE sheet. When the bitumen cracks it imposes a knife edge stress point or line, and since the bitumen has adhered very tightly to the CPE sheet, the gauge length is O. Thus, even a 500 or 1000% elongation is of no avail because there is no free material to allow for any elongation.